(a) Field of the Invention
The present invention relates to a system and a method for measuring the radiation characteristic of an antenna, and more particularly, to an antenna measurement system and an antenna measurement method which speedily measure the radiation characteristic of a source antenna using micro-scaled test antennas and IC chips.
(b) Description of the Related Art
Generally, among the antenna ranges which are used to measure the radiation characteristic (the phase, or the intensity or amplitude) of the antenna, are there a far-field range where the measurement is made while the source antenna is placed far from the tester or receiver antenna, a near-field range where the measurement is made by using the source antenna as a transmitter and taking samples near to source antenna with a probe per a predetermined distance, and a compact range where the measurement is made while the source antenna is placed near to a reflector antenna being the tester antenna.
The far-field range is further classified into an elevated range where the measurement is made while the source antenna and the tester antenna are installed at a tower, a building or the top of a hill, a slant range where the measurement is made while one of the source and the tester antennas is placed at high position and the other on the ground, and an anechoic chamber where the measurement is made in a room having a wall with absorbents for removing the possible reflection. The elevated range and the slant range involve lower cost for the installation and measurement of the relevant elements, but practically require very wide area and high tower, with the disadvantage of being much influenced by the external weather. The anechoic chamber involves the indoor measurement, and is not influenced by the external weather, with the disadvantage in that much cost is needed to make a large laboratory (for example, making it with a vertical length of 10 m, a horizontal length of 10 m and a height of 5 m) with absorbents.
The far-field distance rff between the source antenna and the tester antenna is given by rff=2D2/λ (where D indicates the inter-distance of the source antenna, and λ indicates the operation frequency). As illustrated with the 70 m reflector antenna operated at 2.3 GHz, the far-field distance rff is determined to be 75 km. Accordingly, with the case of the elevated range or the slant range, the distance between the source and the tester antennas becomes enlarged. As various objects such as trees, forests, hills, rivers and buildings are existent between the source antenna and the tester antenna, it is very difficult to make the correct measurement, and to quickly cope with the variable measurement situations. Consequently, the measurement values are largely differentiated due to the difference in the temperature, and the weather. Moreover, with the case of the far-field range, the source antenna is exposed to the outside to obtain the correct measured values, and hence, it becomes difficult in the radar or military antennas to make the desired measurement while keeping a secret.
The compact range is desirably installed within the relatively small space, but it undesirably requires a large-scaled reflector.
With the compact range, the measurement may be made in a very small space provided that the inter-distance of minimally 1 wavelength is made to the source antenna. However, as the probe should precisely move in the X and Y axial directions to correctly figure a predetermined plane (the plane perpendicular to the central axis of the source antenna) within the short distance, much time and cost are consumed to make the equipment for moving the probe (the tester antenna), and to make the desired measurement.
The anechoic chamber also involves the same problem as with the near-field range in that the measurement is made using a probe.
That is, with the case of the near-field range and the anechoic chamber, as the data measured at the probe are all transformed into far-field range data, the correct data can be obtained only when the probe moves very precisely. The precision in the movement of the probe is several micrometers to several tens micrometers. As the carrier for moving the probe very precisely is made with a high cost of up to hundreds of millions, it is practically difficult with the small-scale companies to make measurement experiments related to the development of antennas in a sufficient manner.
As the measurement is made while moving the probe in a slight manner, several hours are consumed even to make the measurement once, and this means that considerable time is wholly needed to complete the required measurements. Furthermore, with the high possibility of making errors in the measuring due to the variable environmental conditions, it becomes impossible to make the total inspection with respect to the produced antennas, and only the deficient sampling test can be made.
In order to obtain more correct far-field range data, it is required to enlarge the mobile range (the plane area) of the probe, but such an enlargement is practically limited due to the carrier for moving the probe.
Furthermore, the carrier for moving the probe is liable to generate electromagnetic waves, which are applied to the measured values as noises.
Furthermore, with the case of the near-field range and the anechoic chamber, as the measurement is made only to the front side of the source antenna, it is impossible to make correct expressions for the back lobe. In order to correctly express the back lobe, it is necessary to directionally reverse the source antenna and make the measurement again, and this involves the long measurement time increased by two times.